The present invention generally relates to a microwave solid-state amplifier, and more particularly relates to an apparatus in which microwave signals in a range from 1 GHz to 50 GHz are amplified by a plurality of solid-state amplifier unit and then combined with each other or a single microwave signal is divided into a plurality of signals and then amplified by a plurality of solid-state amplifier units.
Conventionally, microwave amplifiers have been arranged such that amplifiers constituted by FETs (field effect transistors) are attached on a substrate and a microwave signal is passed through a plurality of amplifying stages so as to derive output power from the final power stage. In a microwave range, however, there is a limit in power derived from a single semiconductor device, and in order to obtain large power in a solid-state amplifier, therefore, there has been used such a device in which the output is added and increased through a power combiner. In this case, as a combiner in which a circuit loss is relatively small and which is suitable for large power, there has been used such a radial cavity power divider/combiner as shown in FIG. 5 (reference is made to IEEE MTT-S DIGEST, 1983 and MICROWAVE JOURNAL, 1984, January). The divider/combiner is constituted by a T.sub.010 mode cavity resonator 52 and a T.sub.020 mode cavity resonator 60 which are disposed vertically with the same center axis. The cavity resonator 52 is coupled with an external line through a coupling probe 53 and a coaxial connector 51, and the cavity resonator 60 is coupled with an external line through a plurality of circularly disposed connecting means constituted by a coupling loop 56 and a coaxial connector 58. The resonators 52 and 60 are coupled through a coupling probe 54 supported by a dielectric supporter 55. A tuning screw 57 is vertically movably disposed at a central portion. In order to realize a high output microwave amplifier by using such a radial cavity resonator as described above, two radial cavity resonators are prepared, one being used as a power divider and the other being used as a power combiner, and a plurality of amplifiers are disposed between the respective coaxial connectors 58 of the two radial cavity resonators.
In the above-mentioned conventional microwave solid-state amplifier, a disadvantage exists in that it is necessary to provide two radial cavity resonators and a plurality of amplifiers which are connected between the power divider and the power combiner through numbers of coaxial connectors, so that the number of terminals for power division and combination is limited by the size of the connectors at a higher frequency and the power loss due to the connectors is increased. That is, the size of the resonator is inverse to the frequency and therefore becomes smaller as the frequency becomes higher. For example, the adjustable size of the tuning screw 57 is predetermined and the size of each of the coaxial connectors 51 and 58 is determined depending on the size of the coaxial cable, so that if the resonator is reduced in size, the number of the attached terminals is limited correspondingly.
Generally, in a cavity resonator, the band width is narrower than 20 GHz at the most. Accordingly, in the resonator shown in FIG. 5, the TM.sub.010 mode cavity resonator 52 and the TM.sub.020 mode cavity resonator 60 are connected so as to make the band width wider through double tuning. If it is intended to widen the band width by double tuning, however, the structure becomes complicated.